1. Field of the Invention
The present invention relates to opto-electronic test systems for automated quality control of two dimensional bodies having a high geometric figure density, and in particular to such a test system which scans a test specimen and undertakes a number of different tests relating to the geometry thereof and stores any errors with associated position coordinates for subsequent visual examination.
2. Background of the Invention
Many defects in two-dimensional elements having high geometric figure density such as, for example, printed circuits, intermediate products utilized in the manufacture of printed circuits, and printing tools, can only be found by means of an optical quality control. Particularly in the quality control of intermediate products such as, for example, structures in developed photo layers, as well as in the case of printing tools, conventional test systems are completely dependent upon the visual inspection of an optical image of the test specimen. Such testing is becoming increasingly difficult and subject to inaccuracies as a result of the continuing efforts to decrease the size of printed circuits and increase the track density. In particular, testing for localized short circuits and track interruptions resulting in open circuits is exceedingly difficult by present methods. Moreover, such conventional methods require a substantial personnel outlay which results in a significant expense and in many instances cannot provide error recognition with the required certainty.
Some attempted solutions to this problem are found in an article in the periodical "Proceedings of the Fourth International Joint Conference on Pattern Recognition," 1978 at pages 970 through 974 wherein a method is described which has application only for testing printing tools, and in the periodical "Feinwerktechnik & Messtechnik," 84 (1976) 7, an article entitled "Automatischer Vektordistanzkomparator VDK Projectina" is found on pages 330 through 334 in which an opto-electronic device is described for testing flat objects having a high geometric figure density such as, for example, masks, hybrid circuits, printed circuits, serigraphs and the like. As described therein, such articles can be automatically tested as to completeness and congruency by means of a comparison with an original master pattern. The system described therein has the significant disadvantage of strong reflection fluctuations which occur in the printed circuits and is admittedly not yet developed for practical commercial use. Moreover, a precise adjustment of the test object within the test system is required for accurate results. Optical and opto-electronic auxiliary testing is therefore still undertaken utilizing, for example, projectors and/or television cameras.